1. Field of the Invention
The present invention relates to a high-frequency signal transmission line and an electronic apparatus including the same, and specifically relates to a high-frequency signal transmission line used for transmission of high-frequency signals, and an electronic apparatus including the same.
2. Description of the Related Art
A conventional high-frequency signal transmission line is disclosed in PCT Publication No. 2011/018934, for example. FIG. 46 is an exploded view of a signal line 500 disclosed in PCT Publication No. 2011/018934.
The signal line 500 illustrated in FIG. 46 includes a body 512, ground conductors 530a, 530b, and 534 and a signal line 532. The body 512 is configured of insulating sheets 522a to 522d being laminated in this order.
The signal line 532 is provided on the insulating sheet 522c. The ground conductors 530a and 530b are provided on the insulating sheet 522b. The ground conductors 530a and 530b face each other via a slit S. The slit S is overlaid with the signal line 532 in planar view from the laminating direction. Accordingly, the ground conductors 530a and 530b do not face the signal line 532.
The ground conductor 534 is provided on the insulating sheet 522d, and faces the signal line 532 via the insulating sheet 522c. 
With the signal line 500 thus configured, the ground conductors 530a and 530b do not face the signal line 532, and accordingly, less capacitance is generated between the ground conductors 530a and 530b and the signal line 532. Therefore, even when reducing an interval in the laminating direction between the ground conductors 530a and 530b and the signal line 532, capacitance generated between these elements is suppressed greatly, and the property impedance of the signal line 532 is prevented from deviating from desired property impedance. As a result thereof, with the signal line 500, reduction in the thickness of the body 512 may be realized.
However, with the signal line 500 disclosed in PCT Publication No. 2011/018934, as will be described below, relatively low-frequency noise readily occurs. Hereinafter, both ends of the signal line 500 will be taken as end portions 540a and 540b, and a portion between the end portions 540a and 540b of the signal line 500 will be taken as a line portion 542.
The signal line 500 has, as illustrated in FIG. 46, an even cross-sectional configuration at the line portion 542. Therefore, the property impedance of the signal line 532 at the line portion 542 is even. On the other hand, the end portions 540a and 540b are inserted into a socket of a circuit board, for example. At this time, a terminal within the socket and both ends of the signal line 532 are connected, and accordingly, parasitic impedance occurs at a connection portion of these elements. Further, the signal line 532 at the end portions 540a and 540b faces a conductor within the socket, and accordingly, parasitic capacitance is generated between the signal line 532 at the end portions 540a and 540b and the conductor within the socket of the circuit board. As a result thereof, the property impedance of the signal line 532 at the end portions 540a and 540b differs from the property impedance of the signal line 532 at the line portion 542.
Here, in the event that the property impedance of the signal line 532 at the end portions 540a and 540b differs from the property impedance of the signal line 532 at the line portion 542, reflection of a high-frequency signal occurs at the end portions 540a and 540b. Thus, standing waves, which have a lower frequency with a ½ wavelength distance between the end portions 540a and 540b, are generated. As a result thereof, low-frequency noise radiates from the signal line 500.